Amplifier



Patented July 2.1,

' UNITED-STATES:

COMPANY, A' 'coRPoRAfrIoN or NEW YoR i AMPLIFIER.

Application med, october 13,1921. serial No. 507,478.

To-aZZ wimmelt may concern: i

Be it known that I,'ALBERT W. HULL, a

citizen vof the United States, residing at Schenectady, in the 'county' of Schenectady,

State of New York, have invented certain new and useful. Improvements in Amplifiers.'

of which the followingis a specification.

lMy present invention relates to vamplifiers, and more particularly to amplifiers of the multi-stage type employing a plurality of eleptron discharge devicesconnected incasca e.

' providel a simple and efficient circuit connection for connecting a plurality of elec# tron discharge amplifiers in cascade.

Another object of my invention-is to provide a multi-stage amplifier capable of giving a high degree of amplification for each stage and at'the Sametime capable of operating with substantially the same efficiency for all frequencies.

In connecting electron discharge amplifiers in cascade in the past itvhas not been customary to operate the grids ofthe amplifiers at theI same potentialas the an'odes of the preceding amplifiers of the series, the connection ybetween stages `having 'been made either by inductive or capacity coupling, or where a direct resistance connection has been made between stages it usually has been found necessary'to employ a battery in the connection between the anode and the grid o f the next succeeding amplifier of the series. tion has been made without a battery' it has been necessary to employ separate filament tfiind platel batteries for the different ampliers.

A.' further object of myinvention is to provide means whereby a direct conductive connection may be made from the anode of one amplifier to the grid of the neXt so that both electrodes will always be at the same potential and at the same time a common filament battery and4 a common plate battery may be employed for all of the amplifiers of the series.

The novel features which I believe to be vcharacteristic, of my invention are set forth One of the objects of iny invention isv tov 'trode 6. l trodes these amplifiers may have an addlcircuit of amplifier 1.

Insome cases where a direct connecto the followingdescription taken in confv i" nection with the accompanying ldrawing vin which Fig. 1 illustrates diagrammatically one way whereby my invention may be carriedv into effect; F ig. 2 shows a. modification and Fig. 3 is a characteristic curve showin current under one condition of operation.

I have indicated in the drawing a cascade connection of three electron discharge amplifiers, 1, 2 andx3, each having the-usuali electron emitting cathode 4:, a discharge con-l trolling grid 5- and an anode or plate electional grid electrode-Z interposed between the relation'between gridv voltage and 'I i In addition to these three 'eleci the grid 5 and anode 6. Current-for heatr` ving thefcath'ode. of all of the ampliers l' may be supplied by a common source 8.

Current for'the plate circuits of all of the amplifiers may be derived from a Sourcev connected to the supply mains 9 and 10 through filtering inductances 11 and capacities. 12. .The potential applied to' the plate circuits. of the amplifiers may if desired be varied vby means of thevaria'ble connection 13 tothe potentiometer 14. 'In most cases,`

however, the potentiometer maybe-omitted.: I

The currents 'to be amplified', -are Aimpressed from conductors 15 and 16 upon the' resistance 17,- which is included in the grid The amplified' currentpin the plate circuit of amplifier 1 flows through the resistance 18 and correspondin amplified potential variations are vroduce upon the anode of amplifier 1. hese tntial variations of the anode of amplifigr 1 are impressed' upon the grid of'am'plifier 2 by means' of the direct conductive elec-v trical connection19. Similarly', the amplified potential variations of the anodeof amplifier 2 produced by the Vamplified current fiowing throughv resistance v20 in the plate circuit are impressed by means of the. directy conductive electrical connection 21 upon thel grid of amplifier 3.

I have indicated in'theplate circuit of amplifier 3 a. telephone receiver 22 for glving an indication of the amplified current flowing in the plate circuit of amplifier 3 1n case the current to be amplified is an audio frequency current. In case the current t0 be amplified is a radio frequency current, the

plate circuit of amplifier 3 may be connected in any desired way with a detector. It w1ll be understood that as many amplifiers as desired may be connected -in cascade and vthat any form of indicating apparatus dein the past it has not been found feasible to anode.

operate the grid of one amplifier at the same potential as the plate of the preceding ampliier unless separate plate batteries were employed for the different amplifiers. This difficulty has been due to the fact that it has not been practical tooperate the grid of the amplifier at a positive potential near that of theplate. Consequently where common plate batteries have been employed it has been found necessary to connect the plate of one amplifier to the grid of the next either by capacity or inductive coupling, or to insert a biasing battery in the grid circuit of the second amplifier. These disadvantages may, in accordance with my invention, be overcome in several ways to permit of the use of co-mmon plate and filament batteries for all of the amplifiers. If the resistance 18 is made of greater value than resistance 20, the drop of potential through resistance 18 will be greater than that through resistance 20, and the anode potential of amplifier 1 will be less than that of amplifier 2. Hence the grid of amplifier 2 may beconnected tothe anode of amplifier 1 and the positive potential of thegrid amplifier 2 will always be less than the potential of the Similarly the resistance of the plate circuit of amplifier 3 may be made less than that of 20 so that the plate potentialof amplifier 3 will always be greater than the grid potential. By progressively decreasing the resistance in the plate circuits of the amplifiers in this way several more stages of amplifiers than those indicated may be operi ated in cascade for a common plate battery with the plate potential ofeach amplicr always higher than the grid potential.

One of the factors which has prevented the successful operation of amplifiers in cascade with the grid operating at about the .same potential as the plate, has been the tendency of the grid to receive current from the plate due to the emissio-n of secondary or impact electrons from the plate which flow to the grid preventing the grid from becoming more positive. This tendency may be overcome and the grids operated normally at about the same potential as the plate by making the plate in such a way that it will not emit any appreciable number of secondary electrons. This may be accomplished in several ways, as for example, by inaking the plate with a black or rough surface or by forming relatively deep and narrow corrugations on its surface. By constructing the plate in such a manner any impact electrons emitted will have diiiculty of all of the amplifiers as connected` directly to the positive terminal of the source which supplies current to the plate circuits. It will be apparent that by this connection the potential of electrodes 7 will be fixed at a positive value which is always higher than that of the anodes 6, whether the potentiometer 14 is -used or omitted. If this potential and the potentials of the anodes are properly chosen advantage may be taken of secondary or impact emission from the anode to produce a high positive resistance or a negative resistance in the plate circuits in accordance with the well known dynatron action, as described in my Patent 1,387,984 of August 16, 1921. The negative resistance may be proportioned to neutralize the positive resistance in the plate circuit and the positive resistance of the grid circuit of the next succeeding amplifier,

and thus greatly increase the degree of amplification per stage which may be obtained. A great increase in amplification over that obtainable without the electrode 7 may be obtained however without the resistances being actually negative provided they are increased from their normal low values to very high positive values. nections to the grid 5 and 7 may be reversed, the grid 5 being maintained at the constant positive potential and the grid 7 serving as a control grid. In this way the grid 7 may be made to have a negative or very high positive resistance.

The capacity effect between grid and anode of a three-electrode device also greatly reduces the possible amplification of thc device when radio frequencies are employed and causes a tendency for the device to produce undesired high frequency oscillations. Both of these difiiculties may also be reduced by the use of the extra electrode 7, which serves as a screen betwe n grid and anode either when maintained at a higher potential than the anode, as indicated in the drawing, or at approximately the same potential, or at a lower potential than the anode, as set forth moreifuHyy and claimed in my copending application, Serial. No. 431,746, filed December 18, 1920.

In case the resistance of the grid circuits of the amplifiers becomes negative or of a higher positive value by reason of the emission of impact electrons from the grids, it may bedesirable to insert positive resistances 23 in the connections 19l and 21, as indicated in Fig. 2. In thiscase the grids will operate at a lower potential than the anodes. This would reduce the amplification if the gri-ds had normal positive resist- If desired, the con-y lim resistance 23' to an anode at a higher po'-v ance characteristics, `but if the grids have negative or approximately infinite lresistance characteristics over the operating range the amplification willnot be reduced 'Under' these circumstances it would bepossible tov operate as many three-electrode amplifiers as desired in cascade with the grid of each amplifier operating at a lower potential than the anode. 1

The' characteristic curve of Fig. 3 represents a grid currenty characteristic' of veryl high positive resistancebetween the points a and o. If such a' gridl is connected by a high tential any postential variations produced on the .anode will be impressed upon the grid i with only slightdimi'nution. For example,

fthe potential-changes of the anode arev suchthat the grid potential tends to increase from ato b,- the current through the resistance 23 will increase by only a small amount i much less than'the relative increase -of po- -through resistance 23 will be correspond-r tential, andthe increased drop of potential cathode and anode, means .forrimpressing' the currents t be amplified between the cathode and one ofthe grids of one of said '.'device`s, a source of potential-connected between the cathode and-anode of saiddevice,

means for impressing upon the -second grid of sai'd"device ahigher positive ot'ential than that impressed upon .the ano e, and a direct conductive electrical connection between the anode'of the first .device'and one i of the grids of as'econdde'vice.

l 2. 4Means for amplifying electric currents comprising a plurality of electron dischage devices each having a. cathode, an' anode and a pair. of grid electrodes interposed between cathode and anode, `means for impressing currents to'be amplified between the-cathode and one of the grids ofone of said devices,

a source ofpote'ntial connected between the cathpde and anode of said device, a high ohmic resistance in a circuit between the A l cathode and anode of said device which includes said source o f potential, means for impressing .upon the second grid of'said device a `l 1ighe r positive potential st han'thatimpressed upon the anode, anda direct conductivel electrical connection vbetween the',

anode vof the first device-.and

one of the grids of `a second device.v

3. Means, for amplifying electriccurrents I comprising a plurality of electron discharge devices each having a cathode, an anode and aj pair of grid electrodesinterposedbetween cathode and anode, means for impressing,

the currents tobe I amplified between the cathode and one'of the grids of one of said I devices,`a source of potentianl connected be# tween the cathode and anode of saiddevice,- means forlmpressing upon; the second grld of said device -a higher s positive potential than that impressed upon the anode, and

means for' directly impressing between the cathode .audone of the grids of a second device potential variations produced between the cathode and anode of the. first device.

l .4. Means for amplifying electric currents comprising a plurality of electron discharge devices each having la cathode, ananode and a pair of grid electrodes interposed between cathode vand' anode, means for impressing currents to be amplified between the cathode and one of the grids of one of said devices,

a source yof potential connected between the cathode and anode of said device, a high ohmic resistancel in a circuit between the Pill cathode and anode of said device which in-v cludes said source of potential, means for impressing upon the second gri-d of said devicea higher positive potential than that. .impressed upon the anode, and means lfor directly impressing between the cathode and one of the grids of a second device potential variations -produced between the cathode and anode o'f the first device.

5. Means for amplifyingelectric currents comprising a plurality of electron discharge devices leach having a cathode, an anode and a pairof grid/electrodes interposed between cathode and anode, means for impressing the' currents to be amplified bet-Ween the lcathode vand the grid ofv said device which .is-nearest the cathode, a source of potential connected between the cathode and anode of said device,means for. impressing upon the second grid ofsaid device a higher positive potential than that impressed upon the lll!) anode, and adirect conductive electrical conf c nection between `the anode o f the first device andone of the grids'of asecond device.

6. Means for amplifying electric currents comprising a plurality of electron discharge devices'each having a cathode, an anode and a pair ofgrid electrodes interposed between cathode and anode, means for impressing currents to be ampliiedbetween the cathode and the grid of said device which is nearest the cathode, a source of potential connected between the cathode and anodeof said de-v vice, a high ohmic reslstance in a circuit between the :cathode and anode of said ldevice which includes said source of potential,

means for impressing upon the-second .grid of said device ahigber positive potential than that impressed upon'theano'de, and a direct Vconductive electrical connection between fthe anode of the first device `and one.l

of the grids 'of a-second device. 7 Means for amplifying electric current vcomprising" a plurality of electron discharge devices each having a cathode, an anode and a'pair of grid electrodes interposed between cathode and anode, means for impressing the currents to be amplified between the cathode and the gi'id of said device which isnearest the. cathode, a source of potential connected between the cathode and anode of said device, means for impressing upon the second grid of `said device a higher positive potential than that impressed upon the anode, and means for directly impressing between the 'cathode and one of the grids of a second device potential-variations produced between the cathode and anode of the first device. *Y

8. Means for amplifying electric currents Y comprising a plurality of electron discharge vdevices each having a cathode, an anode and a pair of grid electrodes interposed between cathode and anode, means. for impressin currents to be amplified between cathode and the grid of said device which is nearest the cathode, a source of potential connected between the cathode and anode of said device, a high ohmic resistance in a circuit between the cathode and anode of said device which includes said source of potential, 'means for impressing upon the second grid of said device a higher positive potential than that impressed Vupon the anode, and means for directly impressing between the cathode and one of the `grids of a second device potentialv cathode and one of the grids of one of said devices,l a source of potential connected be- I'tween the cathode and anode of said device, means for impressing upon the second grid of said device a higher positive potential than that impressed upon the anode, the potentials impressed upon the anode and sec# ond grid being so chosenthat the device has a negative resistance in the circuit between cathode and anode, and a direct conductive electrical connection between the anode of the first device and one of the grids of a second device.

10. Means for amplifying electric currents 'comprising a plurality of electron discharge devices, each having a cathode, an anode and a pair of grid electrodes interposed between cathode and anode, means for limpressing currents to be amplied between cathode and one off the grids of one of said devices, a.` .source vof potential. connected between the cathode and anode of said device, a hi h ohmic resistance in a -circuit between e cathode and anode of Asaid device which 1ncludes said source of potential,` means for impressing uponl the second grid ot said device a higher positive potential than that impressed upon they anode, the potentials impressed upon the anode and second grid being so chosen that the device has a negative resistance in the circuit between cathode and anode, and a direct conductive electrical connection between the anode of therst device and one of the grids of a second device;L

11. Means for amplifying electric currents comprising a plurality of electron discharge devices eachliaving a cathode, an anode and a pair of grid electrodes interposed between cathode and anode, -means for impressing the currents to be amplified between the cathode and one of the grids of'one of said devices, a source of potential connected between the cathode and anode of said device,

,means for impressing upon the second grid 'ot said device a higher positive potential than that impressed upon the anode, the

potentials impressed upon the anode and second grid being so chosen that the device has a negative resistance in thefcircuitlbetween cathode and anode, and means for directly impressing between the cathode and one of the grids of a second device potential variations produced between the cathode and anode of the first device.

12. Means for amplifying electric currents comprising a plurality of electron discharge devices each having a cathode, an anode and a pair ofgrid electrodes Vinterposed between cathode and anode, means lfor 4impressing currents to be am lilied between the cathode and one of the grids of one of said devices,

a source of potential connected between thev ode and anode, and means forfdirectly impressing between the. cathode and one of the grids of a second device potential variations produced between the cathode and anode of A the .trst'device l .l

13. The combination in an amplifying system of a plurality ofelectron discharge amplifiers connectedY in cascade each of which has acathode, an anode and two grids and plate and grid circuits connected between' said cathode and said anode' and one of said. gridsresp'ectively, means for inipressing currents to `be amplified upon the grid circuit of the first .of said amplifiers, means for impressing upon thel second grid offeach of said ampliiiers a higher positive potential than' that impressed upon the .anodsa., and' a direct icon du'f'stive electrical: connection between the anode of each amplifier'of the series exceptthe last and the .first grid of the succeeding'amplifier. v

14. The fcombination in an amplifying g syst'emof aplurality of'electron discharge amplifiers connected- .in cascade each of -wh1ch liai s'a cathode, an anodeand two lgrids and plate and grid circuits connected etween said .cathode and said'anwieandl (-ne. of vsaid grids respectively, high ohmic I -fesistances in each of thev plate circuits except' the last of the series, means .for iinpressing'currents to be amplified upon the grid circuit ofthe 'first of said amplifiers,`

means for impressing upon the second grid of each of 'said amplifiers a higher positive potential than that impressed upon lthe anodes, and a' direct conductive electrical connection between the anode.. of each amplifier of the series except the-last and the Vfirst grid of the succeeding amplifier.

1 5. The combination in an amplifying system lof a plurality/'of electron discharge .amplifiers connecte in cascade, each of fwhich has la cathodejan 'anode and two ids and plate and grid circuits connected etween said cathode and-said anode and one'of said grids respectively, means for inipressing currents to be amplified upon the l grid circuit of the first of said amplifiers,

means for impiessingiipon. the secoiidfgrid of'each of'said amplifiers' a higher positive potential than that impressed upon the 'anodes, and means for impressing' potentialvariations produced :upon the anode of each amplifier except the last'directly uponftlie' grid of the next. succeedingamplifier of the series.l i 1 16. The combination 1n an 'amplifying system ofga'plurality' of electron discharge of said grids respectively, high -ohmic i'e- `ampliers connected in. cascade, each of which has a cathode, an anode and two grids .and plate and gridcircuits connected between'said-cathode and said anode 4and one sistances in eachA of the p latev circuits except the. last ofv the series, means for :im-

" pressing currents to bevamplified upon the.

grid'circuitof -the first of said amplifiers,

means forv impressing'- upon the Asecond grid of each of said amplifiers a higherv positive potential than that. impressed uponl the anodes, and means for impressing 4potential variations producedupon the anode of each amplifier except the lastdirectly upon ther grid of the next 'succeeding amplifier of the series. 1

17. The Combination in 'an amplifying system of a pluralit of electron ldischarge amplifiers connecte in ,-casci'ide;l each of whichfhas a cathode, an .anode vand two Urids'andplate and grid circuits connected I between vsaid cathode. .and said anode and `one of saidvgridsrespectively, means for.

impressing currents to be amplified upon the gridv -circuit of the first of said ampli.-

fiers, means for impressing upon `the second grid -of each of said amplifiers a higher positive potential than that impressed upon theanode, the potentials impressed upon the v'anode and second grid of'each amplifier being so chosen .that each amplifier has a negative resistance in the'plate circuit, and a direct conductive electrical connection between. they anode of each amplifier .of the seriesexcept the last and thev first grid of i 4the succeeding amplifier.

18. The combination inan amplifying system of. a plurality of electron discharge amplifiers connected in cascade each of which has a cathode, an anode and two grids and-plate and' grid circuits connected between said cathode and said anode and one i of said -gridsrespectively, high ohinic re- .sistances in-each of the plate circuits except the last of. the series, means for impressing' system of a plurality of electron discharge amplifiers connectedI in cascade each of which has a cathode, ananode and two grids and plate and grid circuitsl connected between said cathode and said anode andone of said grids respectively, means for 1m` pressing lcurrents to be amplified upon the grid circuit of the first of' said. amplifiers, means for impressing upon the second grid of each of said amplifiers a higher positive potential than that impressed upon the anode,;tl ie potentials impresscl upon vthe anode and second grid of each amplifier being so chosen that each amplifier has a iiega.- v

tive. resistance in the plate circuit,'and means -for -impressing potential variations produced upon the anode ofeach amplifier except the last directly upon the grid of'the next. succeeding amplifier of the series.

20'. The -combination in an amplifying systemof a plurality of electron dischargev amplifiers "connected in cascadel -each of which has va cathode, an anode and two grids and plate and grid circuits connected between said'catho/de and saidv anode and one of'said grids' respectively, high ohmic resistances in each of the plate circuits except the last of' .the series, means vfor. impressing currents to be amplified upon the gridvcircuit of the first of said amplifiers, means for impressing upon the second grid of each of saidamplifiers ahigher positive potential 3 than that impressed upon the anode, `the potentials impressed upon the anode and second grid of each amplifier being so chosen that each amplifier has a negative resistance in the plate circuit, and means for impressing potential variations produced upon the anode of each amplifier except the last directly upon the grid of the next succeeding amplifier of the series.

2l. Means for amplifying electric currents comprising a plurality of electron discharge devices connected in cascade, each having a cathode, an anode and a controlling grid, grid and plate circuits associa-ted with each of said devices, a common source of potential for the plate circuits of all of said devices, separate connections from said source to each device, means for impressing the currents to be amplified upon the grid circuit of the first device, and means for maintaining the grid of each succeeding device at the same potential as the anode of the preceding device.

22. Means for amplifying electricv currents comprising a plurality of electron discharge devices connected in cascade, each having a cathode, an anode and a controlling grid, grid and plate circuits associated with each of said devices, a common source of potential for the plate circuits of all of sai-ddevices. separate resistances in the plate circuit of each device, means for impressing `the currents to be amplified upon the grid circuit of the first device, and means for maintaining the gridof each succeeding device at the same potential as the anode of the preceding device.

23. Means for amplifying electric currents comprising -a plurality of electron discharge `devices connected in cascade, each havinga cathode, an anode and a controlling grid, grid and plate circuits associated with each of said devices, a common source of potential for the plate circuits of all of said devices, separate resistances Iin the plate cir- 'cuit of cach device, the values of saidkresistances progressively decreasing from the rst to the last of the series, means for impressing the currents to be amplified upon the grid circuit'of the first device, and means for maintainingthe grid of each succeeding device at the same potential as the anode of the preceding device.

245. Means for amplifying electric currents comprising a plurality of electron discharge devices each having a cathode, an anode and a pair of grid electrodes interposed between cathode and anode, means for impressing the currents to be amplified between the cathode andone of the grids of one of said devices,'a source of potential conneet/ed between the cathode and anode of said device, means for impressing a constant positive potential upon the second grid of said device, and a direct conductive electrical connection between the anode of the firstde vice and one of the grids of a second device.

25. Means for amplifying electric currents comprising a plurality of electron disl charge devices each having a cathode, an anode and a pair of grid electrodes interposed between cathode and anode, means for impressing the currents to be amplified between the cathode and the gridof said de-` vice which is nearest the cathode, a source of potential connected between the cathode and anode of said device, means for impressing a constant positive potential upon the second grid of said device, and a direct conductive electrical connection between the anode of the first device and one of the grids of a second device.

26. The combination in an amplifying system -of a plurality of electron discharge amplifiers l,connected in cascade each of which has a cathode, an anode and two grids and plate and grid circuits connected loetween said cathode and said anode and one of'said grids respectively, means for imi pressing currents to he amplified upon the grid circuit of the first of said amplifiers,

means for impressing a constant positivepressing currents to be amplified upon the grid circuit of the first of said amplifiers, means for impressing a constant positive potential upon the second grid of each of said amplifiers, and means for normally maintaining thefirst grid of each succeeding device at the same potential as the anode of thepreceding device.

28. The combination in an amplifying system of a plurality ofV electron discharge amplifiers connected in cascade each of .which has a cathode, an anode and two' grids and plate and grid circuits connected between said cathode and said anode and one of said grids respectively, a common source of potential for the plate circuits of all of said devices, means for impressing currents to be amplified upon the grid circuit of the first of said amplifiers, means for impressing a constant positive potential upon the second grid of each of said amplifiers, and a direct conductive electrical connection between the anode of each amplifier of the series except the last and the first grid of the succeeding amplifier.

pressing a constant positive potential* upon the second grid of each of said amplifiers, and means for normally maintaining the grid of each succeeding device at the same potential as the anode of the preceding device.

30. The combination in an amplifying' system of a plurality of electron discharge amplifiers connected in cascade each of which has a cathode, an anode and two grids and plate and grid circuits connected between said cathode and said anode and one of said grids respectively, a common source of potential for the plate circuits of all of said devices, means for impressing currents to beamplified upon the grid circuit of the first of said amplifiers, means for impressing upon the second grid of eachpof said amplifiers a higher positive potential than that impressed upon the anodes, and/a direct conductive electrical connection between the anodeiof each amplifier of the series except the last and the rst grid of the succeeding amplifier.

31. The combination in an amplifying system of a plurality of electron discharge amplifiers connected in cascade each of which has a cathode, an anode and two grids and plate and grid circuits connected betweensaid cathode and said anode and one of said grids respectively, means for impressing currents to be amplified upon the grid cir-f cuit of the first of said amplifiers, means for impressing upon the second grid of each of said amplifiers: a higher positive potential than that impressed upon the anode, the potentials impressed upon the anode and second grid of each amplifier being so chosen that each amplifier has a negative resistance in the vplate circuit, a common source of potential for the plate circuits of all of said devices, and a direct conductive electrical connection between the anode of each am-y plifier of the series except the last and the rst grid of the succeeding amplifier.

32. The combination in an amplifying system of a plurality of electron'discharge amplifiers connected in cascade each of which has a cathode, an anode and two grids and plate and grid circuits connected between said cathode .and said anode and one 'I of said grids respectively, means for impressing currents to be amplified upon the grid circuit of the 'first of said amplifiers, means for impressing vupon the second grid of each of said amplifiers a higher positive potential than that impressed upon the anode, the potentialsl impressed upon the anodey and second grid of each a1 lifier being.l so chosen that each amplifier has a negative resistance inthe plate circuit, a

common source of potential for the plate circuits of all of said devices, and means for normally maintaining the grid of each succeedingdevice at the same potential as the anode of the preceding device.

33. The combination in an amplifying system of a plurality of electron discharge amplifiers connected in cascade each of which has a cathode, an anode and two grids and-'plate -and grid circuits connected betweendsaidfcathode and said anode and one of said gridsf respectively, means for i1n` pressing currents to be amplified upon the grid circuit of thefirst of said amplifiers, means for impressing' upon the second grid of cach of said amplifiers a higher positive potential than that impressed upon the anodes, the .potentials impressed upon the anode and second grid of each amplifier being of such values as to produce a sufficientemission of impact electrons from the anode to substantially change the resistance characteristics of the plate circuit, and a direct conductive electrical 'connection between the anode of each amplifier of the series except the last and the first grid of the succeeding amplifier.

34. Means for ampifying electric currents comprising a plurality of electron discharge devices connected in cascade, each having a cathode, an anode and a controlling grid,

grid and plate circuits associated with each of said devices, lfa common source of potential for the pate `circuits of all of said devices, means for impressing currents to be ampified upon the grid circuit of the first device and means for fimpressing upon the grid of each succeeding device potential variations producedupon the anode of thepreceding device, the potentials of the anode and grid of each of the succeeding devices being of such values as to produce a sufficient emission of impact electrons from the grid to substantially change the resistance characteristic 'of the grid circuit.

In witness whereof, I have hereunto set my hand this 10th day of October, 1921.

' ALBERT W. 

